When water from water bodies such as flowing rivers and lakes, overflows in to the plain areas adjacent to the banks, then it is called a flood. A flood is caused by release of excess water from a reservoir through a dam, or through excess rains along the path of the river.
Storm is the combination of high speed winds, and continuous and heavy rains. It can be due to development of low pressure regions over the sea. The storms include also hails falling at a lot of speed, freezing cold, thunders and lightnings.
A storm is caused due to a disorder in the environment or ecosystem. Flood may be due to insufficient height or a breach in the banks along the rivers or lakes.